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xen-devel
Re: [Xen-devel] blkfront problem in pvops kernel when barriers enabled
On Wed, Sep 07, 2011 at 10:34:49AM -0700, Jeremy Fitzhardinge wrote:
> On 09/06/2011 06:47 PM, Konrad Rzeszutek Wilk wrote:
> > (on 3.1rc2) Looking to xenstore now there is 'feature-flush-cache=1' and
> > no 'feature-barrier'. So it is ok.
> > <scratches head>
> >
> > I can only think of 2.6.38-3 XenOLinux doing it - and it is a bug
> > to do it. It really ought to _not_ advertise 'feature-barrier' and
> > instead advertise 'feature-flush-cache'.
>
> Does that mean that older guests which don't understand flush-cache will
> be left with no way to force writes to stable storage? Seems to me that
Correct.
> even if the backend would prefer flush-cache, it should also advertise
> barriers.
But doing it incorrectly is bad - really bad.
>
> However, that raises the question of how to express the preferred
> mechanism if multiple are available. You could assume that flush-cache
> is always preferred if available, but that's pretty clunky.
That is how I did it in the frontend.
>
> J
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